Manufacture of tungsten powder



Patented" Sept. 1 1925.

hummus m GRAAFF, or nmnnovnn,

nm-nnnnanns, 'Assmnon. TO GENERAL rare commmr, A conroaa'rron or new YORK.

PATENT OFFICE.

MANUFACTURE OF TUNGS'I'EN POWDER.

To all whom, it may concern:

' Be it known that I, ANTONIUS on GRAAFF, a subject of the Queen of the Netherlands, residing at Eindhoven, North Brabant, in the Kingdom of the Netherlands, have invented certain new and usefullmprovements in or Relating to the- Manufacture of Tungsten Powder, of which the following is a specification.

This invention relates to a method of producing tungsten powder. One method for the manufacture of. this powder starts ,from pure tungstic acid whichis prepared by decomposing a pure tungstate with'anaeid. This tungstic acid is then sub acted to a treatment at high temperature in fire-resisting crucibles and is then'reduced'. The powder which results therefrom may be subjected to several mechanical treatments such as pressing, hammering and drawing. The resulting ire is ready to be'mounted in lamps.

Wire thus manufactured shows however several defects; particularly afteroperation of incandescence the Wire is very brittle, robably due tov unequal crystallization.

wing to this decreased mechanical strength, the wire is much less proofagamstshocks such as occur when switching on the current, and therefore the life 1 of the lamp is apt to beshortened.

' order to avoid "these defects, several methods havebeen proposed as for instance the addltlon of silica, SiO (British' latent No. 155851) or of thoria, jThO (United States Patent No. 1201611). to the tungsten material.

With the present invention much results can be obtained according to which instead of starting from, a simple 'tungstic acid, a complex tungstic acid is used, for example a compound containing tungsten and a metalloid, such as silico-tungstie acid, boro-tungstic acid or the. like, or suitable salts thereof There are severalmethods by which tungsten powder may be prepared from these compounds and some are indicated more fully hereinafter but only by way of. example. Y

in the Province of vApplication filed July 20, 1922. Serial No. 576,388.

Example 1.

600 ms of sodium tungstate are dissolved 1n 4000 c. 0. water and neutralized with strong hydrochloric acid to which solution 48 grams water glass and 100 c. c.

acetic acid 98% are added and ELEC- boiled, until strong hydrochloric acid no longer precipitates tungstic acid. After cooling, strong hydrochloricacid is added while stirring. The solution is then .cooled again and subsequently-boiled and saturated with-'aether,

after which 50 gr. of sodium fluoride. is dissolved in the solution.

Three layers are now formed, viz, an upper-layer of aether, then a solution of the sodium salts and then an oily layer, which contains the silicotungstic acid.

The oily-layer," which is formed after about twelve hours is removed with the aid of a siphon and. shaken with double the volume of water' in afterv which again three layers are formed. The intermediate layer is removed and crystallized while being stirred .or agitated in any other way r The light-yellow crystals obtained are first heated for 6 hours to 150? for 3 hours to 250 G. 'Then they are a separating funnel,

C. and then powdered and. heated during anhour-to 1360? 0. Finally with hydrogen.

the powder is reduced.

1200 ms ammonium" tungstate are boiled with 600. grams gelatinous silicic acid in .8 liters of water, until strong hydrochloric acid does not precipitate any moretungstic acid. acid is filtered ofi' vaporization.

and the filtrate dried The white-crystalline mass is then heated Then the'excess of silicic during 12 hours to 0., then coarsely powdered and heated during 3 hours to 450 C. The-light-yellow product is then these pulverized, sifted and reduced in a hydrogen stream.

Example 3.

9000 grams technical .tungstic acid are dlssolved in 17 liters of ammonia (7 liters strong ammonia and 10 liters water) and filtered. The filtrate is boiled with 3000 grams gelatinous. silicic acid until hydrochloric acid no longer precipitates tungstic acid in a small sample. The liquid is evaporated unitl crystallization begins, after which the solution is poured into 1 liter of strong hydrochloric acid while stirring. The white crystals obtained are dried by suction and heated to 100 6., powdered and reduced.

The methods described in examples 2 and 3 have the advantage that the silico tungstate can be reduced at once, so that it is unnecessary as hitherto to decompose the tungsten salts with an acid to obtain pure tungstic acid.

Ezmmple 4.

1000 grams sodium tungstate and 150 grams boric acid are boiled in about 4 liters of water until strong hydrochloric acid no longer precipitates tungstic acid in a small sample.

After cooling, the crystals are dried by suction and the filtrate is boiled again with 700 grams boric acid and strongly heated by vaporization. After again cooling the crystal mass is dried by suction and the filtrate is saturated with act-her. equal volume of strong hydrochloric acid is added and the oil layer is siphoned 03. With an equal volume of water the borotungstic acid is separated out and the aether is driven off by an air stream.

The liquid is vaporized until crystallization begins; the crystals are heated to 150 C. and the tungsten powder obtained reduced with hydrogen.

The tungsten powder obtained in any of methods can, if desired, be treated with hydrofluoric acid in order to drive out any excess of silica SiO The powder'thus obtained is pressed to bars and. after heating and preparing is drawn to wire. During the sinterin process, oxides contained in. the material are va rized. 4 7 he bar of tungsten obtained in the aforesaid manner is c aracterized by a very fine structure. From 5000 to 10000 particles per sq. have been found. e'wire manufactured therefrom was characterized by an Then anequal crystal structure and great pliability whereas the resistance to mechanical influences was materially higher than with wires manufactured according to old methods.

A wire was tested on a special apparatus resisted 250 shocks whereas the wire usually used only withstood one hundred shocks.

A. lamp provided with a filament according to the invention, showed a duration of life three times as great as ordinary lamps burning with the same number of watts per candle power.

It is possible that the molecularly divided silicic acid or boric acid causes these exceedingly good qualities, because it may prevent during the preparation the adhesion of the tungsten particles and consequently the inclusion of impurities. It is also possible that the physical properties of thetungsten so obtained cause the improvement in quality. These are however theoretical suppositicns which do not afi'ect the invention.

urther it is to be observed that tungsten powder obtained by the invention can be used for purposes other than for the manufacture or" drawn wire for electric lamps.

I mean by the appended claims to cover not only the preparation of tungsten from silico-tungstic acid but also as an equivalent the preparation of tungsten from borotungstic acid.

What I claim is: r

l. The process of. preparing metallic tungsten powder for the manufacture of filaments and like bodies which consists in forming silico-tungstio acid, removing byproducts of the reaction whereby said compound is formed, pulverizing said compound and reducing said compound with hydrogen to form metallic tungsten containing silica.

v2., The process of preparing metallic tungsten powder for the manufacture of filaments and like bodies which consists-in treating a tungstate of an alkali metal with a silicon compound capable of forming silico tungstic acid, extracting said acid, crystallizing therefrom silica-tungstic acid,

'heatin said acid at about 100? (1, powdering an finally reducing with hydrogen.

3. The process of preparing tungsten metal which consists in heating an aqueous s0- lution'of ammonium tungstate with gelatinous silicic' acid, removing the resulting silico-turgstic acid, drying the same, powdering: the same and reducing with hydrogen.

In testimony whereof I aflix my signature.

ANTONIUS 15E GRAAFF. 

